This invention relates to locks and, more particularly, to apparatus for retaining the shell in working relationship with its housing in sliding door or plunger locks.
Plunger locks are often used to provide security in conjunction with sliding doors. The locks are generally cylindrical in shape and retained in a bore in the door and oriented substantially perpendicularly to the door panel. A lock housing is attached directly to the door and a shell, or insert, in the housing is responsive to a key and slides perpendicularly to the door between a locked position and an unlocked position. Often a portion of the housing projects from the front of the door panel. The length of the projection depends upon the relative length of the housing and the panel thickness.
In conventional plunger locks, a longitudinal slot is defined by the housing. A tapped hole in the side of the shell retains a screw with a fillister head. The screw head slides in the slot as the shell is moved between the locked and unlocked positions. Thus, the shell and slot combination limits rotational motion of the shell within the housing. Furthermore, when the lock is in the unlocked state, a bias spring urges the shell away from the locked position until the screw head abuts the end of the slot. Thus, the screw and slot combination also establishes the unlocked position.
As mentioned previously, a portion of the housing often projects from the panels retaining the locks. This projection is sometimes great enough that an end of the slot is exposed. When a conventional plunger lock is mounted with an end of the slot exposed and left in the unlocked position, the screw head is exposed. Therefore, persons can remove the screw and thus remove the shell from the housing, surreptiously determine the combination of the locking apparatus and reassemble the lock without detection. Such surreptious action can be avoided by the application of the lock to panels of a thickness sufficient to conceal the screw even when the lock is in the unlocked position. Obviously the range of panel thicknesses to which the locks can be applied with full security is substantially narrowed by the solution. An alternative suggestion is to provide a number of locks with various housing lengths and utilize shorter housings with the thinner panels. This, however, entails increased cost. Furthermore, a complete solution is not provided because extremely thin panels, such as metal doors, still cannot be accommodated. This is because a reduction in housing length also reduces the length of travel of the shell. Thus, insufficient locking action becomes a problem.
It is an object of this invention, therefore, to provide a plunger lock that can be utilized on thin panels with full security.